This invention relates to a secondary battery having a stack of secondary cells each comprising an ion-exchange porous separation membrane.
Porous membranes have been used widely for various purposes in chemical, electrochemical and brewing industries. The thickness, porosity, and pore size of such porous membranes are determined for each purpose. Ion-exchange porous membranes having porous and ion-exchange properties have also been proposed for applications particularly in electrochemical devices. It is the current practice to produce such an ion-exchange porous membrane by applying a physical or chemical process to line or coat an ion exchange material on one or both of the surfaces of a porous membrane. However, a number of problems occur in such prior art multi-layer type ion-exchange porous membranes. First of all, the multi-layer type ion-exchange porous membranes have a relatively great thickness and thus a relatively great electric resistance. Since ion exchange films inherently exhibit a great resistance to ionic migration unlike porous films, it is very difficult, if not impossible, to produce ion-exchange porous membranes having a small electric resistance through such a physical or chemical process lining or coating an ion exchange material on one or both of the surfaces of a porous membrane. In addition, ion exchange films, which are very expensive, have not be used widely in spite of the fact that they have useful functions.